The invention relates to a booster as may be used in a brake of an automobile or the like, and more particularly, to a booster capable of reducing generation of sounds during a suction stroke when a pressure fluid is introduced.
Generally a booster comprises an enclosed vessel formed by a front and a rear shell, a power piston and an associated diaphragm which divides the interior of the enclosed shell into a constant pressure chamber and a variable pressure chamber which are located toward the front and the rear shell, respectively, a valve body disposed adjacent to the inner periphery of the power piston for integral reciprocatory motion therewith, and a valve mechanism housed within the valve body and controlled to be opened or closed in response to a brake pedal operation. When a brake is to be applied, the valve mechanism is opened and closed to introduce the atmosphere into the variable pressure chamber to create a pressure differential between the variable and the constant pressure chamber, which acts upon the power piston to perform a booster function. When the brake is released, the communication between the variable pressure chamber and the atmosphere is interrupted, and the variable pressure chamber is caused to communicate with the constant pressure chamber, thereby allowing the power piston to be returned to its inoperative position under the resilience of a return spring.
A conventional valve mechanism used in a booster as mentioned above is illustrated in FIG. 2, and its construction will be described below. A valve mechanism 13 comprises an annular, first valve seat 14 formed on an end face, in a radially inner region, of a valve body 6 which undergoes a reciprocatory motion within an enclosed vessel (only part of a rear shell 2 being shown), an annular, second valve seat 16 formed on an end face of a valve plunger 15 which is slidably fitted into the valve body 6 in axial alignment therewith, and a valve element 18 disposed inside the valve body 6 and urged by a spring 17 to be seated upon either the first valve seat 14 or the second valve seat 16.
Formed in the valve body 6 are a constant pressure passage 19 which allows a space E.sub.1 radially outward of a first seat S.sub.1 defined by the contact between the first valve seat 14 and the valve element 18 to communicate with a constant pressure chamber, a pressure passage 23 which allows a space E.sub.2 radially inward of a second seat S.sub.2 defined by the contact between the second valve seat 16 and the valve element 18 to communicate with a source of pressure fluid, and a variable pressure passage 21 which allows a space E.sub.3 located between the first seat S.sub.1 and the second seat S.sub.2 to communicate with a variable pressure chamber.
When a conventional booster incorporating the valve mechanism 13 as mentioned above is inoperative, the valve plunger 15 retracts, whereby the valve element 18 is seated upon the second valve seat 16 and is removed from the first valve seat 14, as shown in FIG. 2. Thus, in the inopeative position, the second seat S.sub.2 defined by the second valve seat 16 and the valve element 18 which contact each other is established to close the pressure passage 23 while the first valve seat 16 and the valve element 18, which would define the first seat S.sub.1, are removed from each other, thereby allowing the constant and the variable pressure chamber to communicate with each other through the constant pressure passage 19 and the variable pressure passage 21, thus allowing them to assume an equal pressure.
By contrast, when the booster is actuated, the depression of a pedal acts through an input shaft 25 to drive the valve plunger 15 forward to cause the valve element 18 to be seated upon the first valve seat 14, whereby the contact therebetween establishes the first seat S.sub.1. Accordingly, the constant pressure passage 19 is closed, interrupting the communication between the constant and the variable pressure chamber. A continued advancement of the valve plunger 15 moves the valve element 18 away from the second valve seat 16. When the second seat S.sub.2 is no longer established, the pressure passage 23, which is located radially inside, communicates with the variable pressure chamber 21, which is located outside thereof, whereby the pressure fluid which has passed through the region of the second seat S.sub.2 is introduced into the variable pressure chamber to develop a pressure differential between the constant and the variable pressure chamber, which actuates the booster.
As the pressure fluid from the pressure passage 23 is introduced into the variable pressure chamber after passing through the region of the second seat S.sub.2 in the manner mentioned above, the pressure fluid will assume a vortical turbulent flow (as indicated by an arrow in FIG. 2) at a location in the immediate wake of the exit from the second seat S.sub.2, disadvantageously causing the generation of sounds during the suction stroke.
To accommodate for this, it has been a practice in the art to dispose a sound absorbing member at or near an inlet to the pressure passage 23 which would allow the passage of pressure fluid there through while presenting a resistance to the passage of pressure fluid. The provision of such sound absorbing member is effective to decrease the rate at which the pressure fluid is introduced into the variable pressure chamber through the second seat S.sub.2, thus suppressing the described generation of sounds during the suction stroke.
However, the provision of such sound absorbing member in the pressure passage to retard the rate of the pressure fluid as it is introduced results in a disadvantage that the response of the booster is degraded.